I work by myself, and am always a bit scared of spreading myself too thin, so I have not been to active on the old domain buying front.

Having said that, now would probably be a good time to buy old domains. Jim Boykin again mentioned his new love for oldies and Graywolf said

Came to the same conclusion myself, emailed about 150 people picked up 2 domains from 2000 for under $1K.

Think of how cheap those site purchases are. Decent links can cost $50 to $300 or more each, so buying whole sites for $500 is cheap cheap cheap! How cheap is it? Even the most well known link broker is recommending buying a few old domains.

Why now is the perfect time to buy old domains:

It is right before the Christmas shopping season and many people not monetizing their sites might be able to use a bit of spare cash.

Many older domains are doing better than one would expect in Google's search results, which means they may recoup their costs quickly.

As Andy Hagans said, "Some older sites seem to be able to get away with murder in Google's search results."

Link popularity flowed much more naturally to commercial sites in the past than it does now. This means buying something with the a natural link profile may be far cheaper than it would be to try to reproduce similar linkage data.

At different times search algorithms show you different things. Before the Christmas shopping season each of the last few year it seems Google rolled out a new algorithm that wacked many sites which SEO'ed their way to the top (IMHO via link trading and low quality linkage data). Most of the algorithm changes are related to looking at linkage quality, communities, and ways to trust sites. The most recent update seems to have (at least temorarily) dialed up the weighting on TrustRank or a similar technology, which has had the net effect of highly ranking many old/trusted/authoritative sites that may lack some query specific authority. If you shop for sites that fit the current Google criteria well then add some good SEO to it you should be sitting good no matter which way the algorithms slide.

I recommend that everyone spend their full attention coming up to speed on beta.search.msn.com.

It's very rare to get to see a search engine in transition, because that's the best time to see what the different criteria are for ranking.

Now that Google is in a state of flux it might be a good time to perform many searches to look for some underpriced ad inventory. If you know what you are looking for you are more likely to find it in the organic search results than in the AdWords system.